It is very important that offshore installations in ice-filled waters are protected against the impacts of the ice. For instance, an oil or gas platform may be concerned. Typically, floating ice drifts with the current, but it is also influenced by the wind. The ice may come in large chunks or pieces, or ice floes, which can cause damage to ocean-going vessels and offshore platforms such as a drilling platform or drilling vessel. Further, it is known that coherent ice floes normally have greater strength than ice floes that are broken or partially broken.
In order for a large drilling vessel to operate, it must not be significantly affected or damaged from impact by drifting ice floes. Upon impact, a drilling vessel must usually not be shifted more than about 2% of the depth of the water before the drilling operation has to be discontinued, and, if it is shifted more than about 5%, the drill pipe must usually be disconnected. It is therefore to be understood that impacts from ice, in particular in shallow waters, are extremely critical. Under no circumstances should large pieces of ice be allowed to hit the drilling vessel.
It is known within the prior art to use several, typically three, powerful icebreakers that cooperate to manage ice and ensure that large chunks of ice cannot drift towards the platform or that the ice is not capable of packing around it. These vessels utilize their own motive power.
Pack ice and ridged ice are the types of ice that require the largest amount of energy to avoid. It is assumed that by means of conventional icebreakers it may be necessary to use machine power of upwards of 60-70 Megawatts, when the ice is thick and the current is heavy. That magnitude of machine power is comparable with nuclear-powered vessels, and in view of the fact that three vessels are often used, it will be understood that it is extremely resource-demanding and cost-intensive to secure a drilling vessel against the impacts of the ice.